258 EXPERIMENTAL PHYSIOLOGY. 



spasms or general tetanus of the whole body. During 

 the paroxysm of convulsions, the limbs are stretched out, 

 extended, hard, and rigid, while the trunk is similarly 

 affected. The extensor muscles are more affected than 

 the flexors. The tetanic paroxysm passes off, to be soon 

 followed by another on the slightest stimulation. 



(c.) Destroy the spinal cord with a seeker or long pin. 

 At once the spasms cease. Strychnia, therefore, acts on the 

 cord directly, and not on the muscles and nerves. 



6. Action of Potassic Chloride or Bromide. 



(a.) Prepare a reflex frog as in Lesson LVIIL, 1. Test 

 the latent period with dilute sulphuric acid, 0'2 per cent., 

 until constant results are obtained. Inject 2 minims of a 

 1 per cent, solution of KC1 or KBr, and after ten minutes 

 test again the latent period. Within a short period the 

 latent period will be greatly prolonged. 



7. Knee- Jerk. 



(a.) Sit on a chair and cross the right leg over the left one. 

 With the tips of the fingers, or a percussion hammer, strike 

 the right ligamentum patellae. The right leg will be raised 

 and thrown forward with a jerk owing to the contraction 

 of the quadriceps muscle. An appreciable time elapses 

 between the striking of the tendon and the jerk. The knee- 

 jerk is almost invariably absent in cases of locomotor ataxia, 

 while it is greatly exaggerated in some other nervous affec- 

 tions, so that its presence or absence is a most important 

 clinical symptom. 



LESSON LIX. 



NERVE ROOTS REACTION TIME. 



1. Functions of the Roots of the Spinal Nerves. To expose the 

 roots destroy the brain of a frog, lay it on its belly, and make a 

 median incision in the skin of the back, from the neck to the 



